Current drug development platforms such as two-dimensional (2D) in vitro cell culture systems and in vivo animal studies do not accurately predict human in vivo effectiveness of candidate therapeutics. These cell culture systems have limited similarities to primary human cells and tissues as only one cell type is employed, and animal studies have a generally limited ability to recapitulate human drug response as different species have differences in metabolism, physiology, and behavior. Many experimental drugs fail in clinical studies due to the inability of current screening technologies, such as in vitro laboratory tissue analysis and animal studies, to accurately predict how the drugs will behave in people.
Therefore, the drug discovery and development fields need an in vitro platform to test candidate therapeutics for better predictions of human response. Current in vitro systems (e.g., rotating bioreactors, suspension of spheroids, and growth on a porous scaffold) are limited in size (1-2 mm) and tend to be two dimensional. Attempts at 3D tissue constructs have had only limited success and have been very small or had a short life-span. The failure of these tissue models are due, at least in part, to the absence of a model vascular system to allow diffusion of oxygen and nutrients into the tissue to support more substantial, natural, sustained, tissue growth.